First Large-Scale Breakdown of Yr15 Resistance to Wheat Yellow Rust (Puccinia striiformis f. sp. tritici) Recorded Globally

The United Kingdom Cereal Pathogen Virulence Survey (UKCPVS) was established in 1967 following a major yellow rust outbreak on the previously resistant wheat variety Rothwell Perdix. Since then, virulence in Puccinia striiformis f. sp. tritici (Pst), the causal agent of yellow rust, has been routinely monitored across the UK.In late winter to early spring 2025, unusually high levels of yellow rust infections on winter wheat varieties previously rated as highly resistant at both seedling and adult plant stages were observed in the counties of Northumberland and Tyne and Wear (Figure 1a). This indicated a potential major resistance breakdown, a concern soon confirmed by reports from across the agricultural industry. Importantly, disease persisted in many of these varieties to the adult plant stage (Figure 1b,c). Through the UKCPVS, urediniospores were multiplied from infected wheat samples by inoculation onto plants of the universally susceptible variety Victo maintained under controlled environment conditions until sporulation was observed. Following multiplication, three early-season Pst isolates (WYR25-001, WYR025-025 and WYR25-034) recovered from previously highly resistant varieties KWS Dawsum, Champion and KWS Palladium were virulence phenotyped on a set of 18 wheat differential lines with known yellow rust resistance genes (Yr), revealing that all were virulent to Yr15 (Figure 2; data not shown). The Yr15 resistance gene, first introgressed into bread wheat (Triticum aestivum) from wild emmer (Triticum dicoccoides) in the late 1980s (Gerechter-Amitai et al. 1989) and widely deployed in breeding since the late 1990s, has provided nearly complete, broad-spectrum, all-stage resistance against Pst for over three decades. Subsequent genotypic analysis through full transcriptome sequencing (Hubbard et al. 2015) of two Yr15-virulent Pst isolates (WYR25-001 and WYR25-025) confirmed these likely evolved from diversification within the PstS10/Warrior(-) lineage, rather than through an exotic incursion (Figure 3).